If i may chip in, in that case i would rather use a "Scene Complication", something the guys at MarvelPlotPoints are using in their Secret War Event.
I'm making rules for this as i go along so bear with me, because i fear if i don't this thread will have 4 more pages to read if i take more time to think about it
Setting one up would require spending a Doom dice, like for a new Scene Distinction (OM17), but that could start at d6, like for complications (OM29).
Here, after the Hulk starts pounding at everything, let's say we have : Civilians in Harm's Way at d8 to make things interesting.
Since complications usually target a specific hero/villain in order to hinder his actions, the Watcher could offer a PP to heroes willing to be burdened by it (meaning they actively try to save them while battling the Hulk)... even more interesting
To simulate unwillingly caused Collateral Damage from SFX such as Berserk or Unleashed, the Watcher simply has to use those die returning to the Doom Pool as effect dice to boost the complication, while the heroes try to get rid of it with their actions (OM54).
The same kind of upgrade could also simulate time-delayed results, like Cam also alluded to in a previous post, by having the Watcher either, step up the complication die by +1 after a set number of rounds, or using Doom dice from the pool at appropriate times to do it, until it ultimately breaches the d12 limit, usually ending the scene in some way
I think that covers it